This invention relates generally to gas furnaces and more particularly to the operation of a smart inducer motor so as to provide constant combustion air flow regardless of various conditions both external to and internal to a induced-draft gas furnace.
In the operation of an induced-draft gas-fired furnace, combustion efficiency can be optimized by maintaining the proper ratio of the gas input rate and the combustion air flow rate. Generally, the ideal ratio is offset somewhat for safety purposes by providing for slightly more combustion air (i.e., excess air) than that required for optimum combustion efficiency conditions. In order that furnace heat losses are minimized, it is important that this excess air level is controlled.
In practice, the rate of combustion air flow is affected by a number of factors including vent length, furnace size, and wind conditions. Although furnace size may be predetermined at the factory, vent length is commonly not known until actual installation time, and wind conditions are normally highly variable during operation of the furnace. Additional conditions such as partial blockages by debris of various kinds can also affect combustion air flow rate while the furnace is in operation.
In addition, a large number of different furnace models are commonly in use at present, and it is highly desirable to provide a method which can be adapted to both a variety of different furnace models currently in use, as well as those that may be manufactured in the future. More specifically, it is desired to have a method of providing excess air control in both two stage and single stage products, as well as in both condensing and mid-efficiency furnaces.
Finally, different benefits may be derived from using the method of this invention depending upon the nature of the furnace in which it is used. Such benefits include the possibility of increased efficiency, lower operating cost, a higher degree of flexibility as to mode of installation, and less noise.